1. Field of the Invention
The present invention relates to an ink jet print head for use in an office or industrial environment, and also to a method of producing the ink jet print head.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing an example of a conventional ink jet print head. The ink jet print head includes an orifice plate 102 formed with a nozzle 101, a chamber plate 104 formed with a pressure chamber 103, a restrictor plate 106 formed with a restrictor 105, a diaphragm/filter plate 109 formed with a diaphragm 107 and a filter 108, a housing 111 formed with a common ink channel 110, a piezoelectric element 112, and a piezoelectric element fixing plate 113 for fixing the piezoelectric element 112 in place. The piezoelectric element 112 is made up of a number of plate-shaped piezoelectric material pieces and a number or electrodes alternately stacked one on the other. For the sake of brevity, the piezoelectric element will be hereinafter referred to simply as xe2x80x9cpiezoelectric elementxe2x80x9d.
The housing 111 includes edges X1 and Y1 for setting the position of the piezoelectric element fixing plate 113 in the X and Y directions, respectively. The piezoelectric element fixing plate 113 is abutted against and fixed to the edges X1 and Y1 by adhesive (not shown). The adhesive must be applied according to the machining precision or the positioning edges X1, Y1 and must be applied thinly.
However, in order to reduce variation in ink ejection, the diaphragm 107 and the piezoelectric element 112 need to be attached to each other with great positional accuracy. This requires that the housing 111 and the piezoelectric element fixing plate 112 be machined with extreme precision. For example, the distance from the positioning edge Y2 of the piezoelectric element fixing plate 113 to where the piezoelectric element 112 is adhered to the diaphragm 107 must be extremely precise so the positioning edges X1, Y1 must be machined in the housing 111 with extremely high precision. Also, the corners between various surfaces must be extremely close to perfect right angles. If not, the surface X1 adhered to the piezoelectric element fixing plate 113 will lean toward or away from the diaphragm 107, so that the surface of the piezoelectric element 112 that is adhered to the diaphragm 107 will also slant with regard to the diaphragm 107. Full and uniform contact between the adhered surfaces of the piezoelectric element 112 and the diaphragm 107 cannot be achieved.
If the adhesive layer is too thin or non-uniform, then the piezoelectric element fixing plate 113 cannot be adhered in accordance with the reference edges X1, Y1. As a result, the adhering surfaces of the diaphragm 107 and the piezoelectric element 112 will not contact each other uniformly, resulting in the diaphragm 107 and the piezoelectric element 112 being adhered to each other at a slant.
When the housing ill and the piezoelectric element fixing plate 113 are made from different materials having different thermal expansion coefficients, then the ink jet head can suffer from warping if the piezoelectric element fixing plate 113 is fixed to the housing 111 by adhesive, for example. The warping can result in variations in ink ejection properties, especially at the end nozzles.
For these reasons, in order to reduce variation in ink ejection, the precision of all components and the thickness of the adhesive must be managed carefully. Components such as the housing 111 and the piezoelectric element fixing plate 113 must be made with high machining precision and so are expensive. As a result, the ink jet head is expensive to make.
In view of the foregoing, it is an object of the present invention to overcome the above-described problems and to provide an inexpensive ink jet print head with reduced variation in ink ejection properties and a method of manufacturing the ink jet print head.
In order to achieve the above and other objects, an ink jet print head according to the present invention includes a pressure chamber portion, an orifice plate, a restrictor plate, a diaphragm, piezoelectric elements, a piezoelectric element fixing plate, a housing, and a cover.
The pressure chamber portion has pressure chambers. The orifice plate is formed with nozzles in a one-to-one correspondence with the pressure chambers. Each nozzle brings a corresponding pressure chamber into fluid communication with atmosphere. The restrictor plate is formed with ink channels in fluid communication with the pressure chambers. The diaphragm forms a side of the pressure chambers. The piezoelectric elements are attached to the diaphragm in a one-to-one correspondence with the pressure chambers. Each piezoelectric element generates, through the diaphragm, a pressure fluctuation in a corresponding pressure chamber when applied with an electric signal. The piezoelectric element fixing plate is fixedly attached to and supports the piezoelectric elements.
The housing includes a common ink channel portion and internal side walls. The common ink channel portion is formed with a common ink channel in fluid communication with the channels in the restrictor plate. The internal side walls adjoin the diaphragm at one side to define a space that opens at an end opposite from the diaphragm. The piezoelectric element fixing plate and the piezoelectric elements are disposed at least partially in the space with a gap existing between the piezoelectric element fixing plate and the internal side walls that define the space.
The cover covers the piezoelectric element fixing plate. The cover is connected to the housing and is provided with an internal space large enough to maintain a gap between the cover and the piezoelectric element fixing plate.
With this configuration, the cover covers the piezoelectric element fining plate and moreover has an internal space large enough so that the piezoelectric element fixing plate can be inserted into while the gap is maintained between the housing and the piezoelectric element fixing plate. Because the internal space in the cover is, in the same manner as the opening in the housing, larger than the both piezoelectric element and the piezoelectric element fixing plate to which the piezoelectric element is fixed, the ink seal and the cover can be fixed on the housing without any external pressure being applied to the piezoelectric element fixing plate. As a result, the ink jet print head is less expensive and has fewer variations in ink ejection properties.
According to a method of the present invention, a piezoelectric element set, a front end set, and a positioning plate are prepared, but not necessarily in this order.
The piezoelectric element set includes a piezoelectric element fixing plate and piezoelectric elements. The piezoelectric elements are attached to the piezoelectric element fixing plate with a predetermined positioning.
The front end set includes a pressure chamber portion, an orifice plate, a restrictor plate, a diaphragm, and a housing. The pressure chamber portion has pressure chambers with positioning that corresponds to positioning of the piezoelectric elements on the piezoelectric element fixing plate. The orifice plate is formed with nozzles in a one-to-one correspondence with the pressure chambers. Each nozzle brings a corresponding pressure chamber into fluid communication with atmosphere. The restrictor plate is formed with ink channels in fluid communication with the pressure chambers. The diaphragm forms a side of the pressure chambers.
The housing of the front end set includes a common ink channel, a space, and positioning holes. The common ink channel is in fluid communication with the channels in the restrictor plate. The space is defined by internal side walls that adjoin the diaphragm at one side. The space is open at an open end thereof opposite from the diaphragm. The space is large enough to insert through the open end the piezoelectric elements and the piezoelectric element fixing plate until the piezoelectric elements contact the diaphragm, while a gap is maintained between the side walls and the piezoelectric element fixing plate. The positioning holes are disposed with a predetermined positioning.
The positioning plate includes dummy chambers and positioning holes. The dummy chambers have positioning that corresponds to positioning of the pressure chamber in the pressure chamber portion. The positioning holes have positioning that corresponds to positioning of the positioning holes.
Once the piezoelectric element set, the front end set, and the positioning plate are prepared, the positioning holes of the positioning plate are mounted on positioning pins or a positioning jig. The positioning pins of the positioning jig have a fixed positioning that corresponds to the positioning of the positioning holes of the positioning plate.
Then, the piezoelectric elements of the piezoelectric element set are aligned with the dummy chambers of the positioning plate while observing the piezoelectric elements through the dummy chambers of the positioning plate.
Next, the positioning plate is removed from the positioning jig and the front end set is mounted on the positioning jig. The front end set is mounted on the positioning jig by mounting the positioning holes of the housing on the positioning pins of the positioning jig.
Next, adhesive is coated on either the diaphragm of the front end set or the piezoelectric elements of the piezoelectric element set.
Next, the positioning jig is used to move the front end set toward the piezoelectric element set, while maintaining alignment between the front end set and the piezoelectric element set, until the piezoelectric element set passes into the space and the diaphragm and the piezoelectric elements contact each other.
Then, the front end set and the piezoelectric element set are removed from the positioning jig. The piezoelectric element fixing plate is covered with a cover while maintaining a gap between the cover and the piezoelectric element fixing plate. The cover is attached to the front end set while maintaining the gap between the cover and the piezoelectric element fixing plate.
With this method, the piezoelectric element fixing plate is covered with the cover while the gap is maintained between the cover and the piezoelectric element fixing plate. As a result, the cover can be fixed on the housing without any external pressure being applied to the piezoelectric element fixing plats. Also, the ink jet print head is less expensive and has fewer variations in ink ejection properties. Further, in the case when sealing is applied to prevent ink leaks, the cover prevents any external pressure from being applied to the piezoelectric element fixing plate.
Because the piezoelectric elements are already properly positioned with respect to the positioning plate the front end set and the piezoelectric element set can be adhered to each other with accurate positioning by bringing the adhesive-coated front end set and the piezoelectric element set into contact with each other to adhere them together. At this time, the front and set and the piezoelectric element set are positioned with the gap between the side walls of the housing and the piezoelectric element set.
Because the positioning jig is used to position the piezoelectric elements with respect to the diaphragm, that is, as represented by the positioning plate, the piezoelectric element can be positioned accurately with respect to the diaphragm even if the various components have variation in machining precision, because the actual positioning is performed using the positioning jig while observing relative positions of the diaphragm and the piezoelectric element. There is no need to provide a highly accurate positioning reference surface in the housing or manage the thickness of adhesive and the like in the manner of the conventional ink jet print head.
Further, because the gap is maintained between the housing and the piezoelectric element fixing plate, the housing and the piezoelectric element fixing plate do not contact each other. Therefore, no warping will occur from differences in expansion even if the housing and the piezoelectric element fixing plate are formed from different materials with different expansion coefficients. Therefore, the ink jet print head can be made inexpensively and with reduced variation in ink ejection properties.